His first comment on looking around him was, "We're not going to have to walk far to pick up rocks."

Drama

It was the end of a seven-hour drama which began at 2036 BST (1936 GMT) the previous evening, when an engine on the command module, Casper, malfunctioned after it had separated from the lunar module.

If the engine had been fired at this point, the craft could have veered out of control or far off course, with disastrous consequences.

The command module has to place itself in a precise orbit above the Moon to be in the right place to pick up the lunar module for the journey home.

As the engine could not be fired, Orion could not be cleared for the landing, and there were serious doubts at mission control that it would be possible to make a landing at all.

Although the astronauts were not believed to be in personal danger, there were fears of another expensive failure like Apollo 13 two years ago, when an explosion on board crippled the spacecraft, aborting the mission and putting its crew at serious risk.

Deadline

The two Apollo 16 astronauts on the lunar module were told to halt their landing attempt and keep Orion close to Casper in a "station keeping position" in which it would be possible quickly to link the two craft if necessary.

Mission control issued an 0814 BST (0714 GMT) deadline to fix the problem or abandon the mission and return to Earth.

Then shortly before 0300 BST (0200 GMT) the command module pilot, Thomas Mattingly, managed to fire the engine while on the far side of the Moon, out of radio contact.

The command module smoothly moved to the right point orbiting between 60 and 70 miles (95 to 110 km) above the lunar surface.

That cleared the way for the lunar module to begin making its descent.

The delay meant Young and Duke have had to cancel one of their three excursions on the moon buggy they have brought with them, but they should still be able to complete most of the mission as planned.

In Context
The command module pilot who dealt with the engine crisis, Thomas Mattingly, was the astronaut who was taken off the disastrous Apollo 13 mission at the last minute.

The Apollo 16 mission was dogged by major and minor setbacks, but scientifically it was a great success.

It brought back more data than ever before, including 212lbs (96 kg) of moon rock.

The two astronauts took two long drives into the lunar highlands, going higher above the lunar plain and into more rugged terrain than other expeditions.

Their findings challenged the geologists' view that volcanic activity had formed the Moon's features.

Instead, they found evidence that the impact of meteorites may have played a larger part than previously thought.

The Apollo programme had already been cut back severely by the time of Apollo 16, and there was only one more manned mission to the Moon, in December 1972.

However, in January 2004 the US President, George Bush, said American astronauts would return to the Moon by 2020 as the launching point for missions further into space.